Reduction Of Positive Charge Research Articles

Tunable pH Sensitive Lipoplexes.

To provide long circulating nanoparticles able to carry a gene to tumor cells, we have designed anionic pegylated lipoplexes which are pH sensitive. The reduction of positive charges in nucleic acid carriers allows reducing the elimination rate, increasing circulation time in the blood, leading to improved tumor accumulation of lipid nanoparticles. Anionic pegylated lipoplexes have been prepared from the combined formulation of cationic lipoplexes and pegylated anionic liposomes. The neutralization of the particle surface charge as a function of the pH was monitored bydynamic light scattering in order to determine the ratio between anionic and cationic lipids that would give pH-sensitive complexes. This ratio has been optimized to form particles sensitive to pH change in the range 5.5-6.5. Compaction of DNA into these newly formed anionic complexes was checked by DNA accessibility to Picogreen. The transfection efficiency and pH-sensitive property of these formulations were shown in vitro using bafilomycin, a vacuolar H+-ATPase inhibitor.

Multiscale Investigation of a Bioresidue as a Novel Intercalant for Sodium Montmorillonite

This paper investigates the efficacy of a novel bioresidue (made from biomass) for organic modification of sodium montmorillonite clay. To this end, montmorillonite was biomodified using a solution-intercalation processing technique. The results of experiments, carried out using techniques of XRD, FTIR, TGA, and oscillatory rheometry, showed that strong interactions exist between certain molecular species of bioresidue (e.g., amide and carboxyl groups) and silicate platelets of montmorillonite clay, leading to a highly intercalated clay structure. An atomic-level analysis using density functional theory (DFT) was also employed to study the effect of the bioresidue’s polar functional groups on the basal d-spacing of montmorillonite. On the basis of DFT results, the overall increase in the gallery spacing observed for amide and carboxyl intercalants could be attributed to the ion–dipole and dipole–dipole interactions and, most importantly, reduction in positive charge of the gallery space. This reduction of...

Effects of Chemical Treatments and Ultrathin Al2O3 Deposition on InAlN Surface Investigated by X-ray Photoelectron Spectroscopy

The effects of chemical treatments and Al2O3 deposition on the InAlN surface were investigated by X-ray photoelectron spectroscopy (XPS). Independent of the extent of native oxide removal, the In 4d core-level binding energy was the same for untreated, HCl-treated, and HF-treated InAlN. This indicated a strong pinning tendency of the Fermi level at the InAlN bare surface. However, a 300 meV decrease in the In 4d binding energy was observed after atomic layer deposition (ALD) of Al2O3, which indicated an increase in the negative surface potential at the InAlN surface. The reduction of positive charge at the InAlN surface is discussed.

Influence of gamma irradiation on the C-V characteristics of the Al/SiNx/Si MIS capacitors

The authors studied effects of gamma radiation on the electrical properties of the MOS capacitor made on SiNx thin films with thickness of 100 nm deposited on p-type (100) silicon wafer using plasma-enhanced chemical vapor deposition method. The authors investigated the chemical bonds and their densities inside the films using Fourier transform infrared (FTIR) spectroscopy. The as-deposited and annealed samples with Al/SiNx/Si structure as metal–insulator–semiconductor (MIS) capacitors were exposed to a 60-Co gamma radiation source with a dose rate of 0.015 Gy/S. The authors performed capacitance-voltage measurements at frequencies 10, 100, and 1000 kHz before and after radiation exposure with doses of up to 40 Gy. It was found that before gamma irradiation compared with as-deposited sample, the annealed samples exhibit less negative flatband voltages (Vfb) shift. This indicates the relative reduction in positive charge in the SiNx:H samples. After gamma irradiation, for all samples a negative shift has been observed in Vfb, being more pronounced in the samples annealed at 700 °C. The more striking feature is that the amount of shift does not change by increasing radiation dose after first irradiation, in which we attributed what to the radiation hardening in Al/SiNx/Si MIS capacitors.

Transportation of carriers in silicon implanted SiO 2 films during ionizing radiation

Silicon ion implantation has been proved to be an effective method for total-dose hardening of SiO 2 in MOS devices such as buried oxides in SOI devices, while the mechanisms are still in discussion. In this work, behavior of 10 keV X-ray induced carriers in silicon implanted thermal SiO 2 was investigated by comparing with Ar implanted SiO 2. Photoluminescence (PL) spectroscopy and TRIM calculation were used to characterize the defects of the ion implanted SiO 2 films. Metal–Oxide–Semiconductor (MOS) structures were fabricated for electrical characterization of the oxides. Positive or negative gate bias was applied during the irradiation to control the separation and transportation of radiation induced electrons and holes. Flatband voltage shifts and are extracted from high frequency capacitance–voltage (C–V) measurement results which are taken prior to and after certain total dose irradiation. The experiment result shows that both Ar and Si implantation and followed anneal could eliminate the net positive charge in SiO 2 irradiated by X-ray. But different with Ar implanted oxide, in Si implanted oxide, the reduction of positive charge is highly dependent on the implanted Si ion fluence, and is well consistent with silicon nanoclusters evolvement tendency. From these results we conclude that along with increased electron trapping at the nanostructures which is suggested by previous studies, enhanced hole trapping and recombination caused by implantation induced vacancy defects are critical mechanism of reduced total ionizing dose effects on Si implanted oxides.

The crystal structure of Haloferax volcanii proliferating cell nuclear antigen reveals unique surface charge characteristics due to halophilic adaptation

BackgroundThe high intracellular salt concentration required to maintain a halophilic lifestyle poses challenges to haloarchaeal proteins that must stay soluble, stable and functional in this extreme environment. Proliferating cell nuclear antigen (PCNA) is a fundamental protein involved in maintaining genome integrity, with roles in both DNA replication and repair. To investigate the halophilic adaptation of such a key protein we have crystallised and solved the structure of Haloferax volcanii PCNA (HvPCNA) to a resolution of 2.0 Å.ResultsThe overall architecture of HvPCNA is very similar to other known PCNAs, which are highly structurally conserved. Three commonly observed adaptations in halophilic proteins are higher surface acidity, bound ions and increased numbers of intermolecular ion pairs (in oligomeric proteins). HvPCNA possesses the former two adaptations but not the latter, despite functioning as a homotrimer. Strikingly, the positive surface charge considered key to PCNA's role as a sliding clamp is dramatically reduced in the halophilic protein. Instead, bound cations within the solvation shell of HvPCNA may permit sliding along negatively charged DNA by reducing electrostatic repulsion effects.ConclusionThe extent to which individual proteins adapt to halophilic conditions varies, presumably due to their diverse characteristics and roles within the cell. The number of ion pairs observed in the HvPCNA monomer-monomer interface was unexpectedly low. This may reflect the fact that the trimer is intrinsically stable over a wide range of salt concentrations and therefore additional modifications for trimer maintenance in high salt conditions are not required. Halophilic proteins frequently bind anions and cations and in HvPCNA cation binding may compensate for the remarkable reduction in positive charge in the pore region, to facilitate functional interactions with DNA. In this way, HvPCNA may harness its environment as opposed to simply surviving in extreme halophilic conditions.

Facile Synthesis of Mesoporous Silica Sublayer with Hierarchical Pore Structure on Ceramic Membrane Using Anionic Polyelectrolyte

A facile method for introducing mesoporous silica sublayer onto the surface of a ceramic membrane for use in liquid-phase separation is described. To reduce the electrostatic repulsion between the mesoporous silica sol and the ceramic membrane in highly acidic conditions (pH < 2), thus facilitating the approach of hydrolyzed silica sol to the surface of the membrane, poly(sodium 4-styrenesulfonate) (Na+PSS-, denoted as PSS-) was used as an ionic linker. The use of PSS- led to a significant reduction in positive charge on the ceramic membrane, as confirmed by experimental titration data. Consistent with the titration results, the amount of mesoporous silica particles on the surface of the ceramic membrane was low, in the absence of PSS- treatment, whereas mesoporous silica sublayer with hierarchical pore structure was produced, when 1 wt % PSS- was used. The results show that mesoporous silica grows in the confined surface, eventually forming a multistacked surface architecture. The mesoporous silica sublayer contained uniform, ordered (P6 mm) mesopores of ca. 7.5 nm from mesoporous silica as well as macropores ( approximately mum) from interparticle voids, as evidenced by transmission electron microscopy and scanning electron microscopy analyses. The morphologies of the supported mesoporous silica could be manipulated, thus permitting the generation of uniform needlelike forms or uniform spheroid particles by varying the concentration of PSS-.

RNA incorporation is critical for retroviral particle integrity after cell membrane assembly of Gag complexes.

The nucleocapsid (NC) domain of retroviruses plays a critical role in specific viral RNA packaging and virus assembly. RNA is thought to facilitate viral particle assembly, but the results described here with NC mutants indicate that it also plays a critical role in particle integrity. We investigated the assembly and integrity of particles produced by the human immunodeficiency virus type 1 M1-2/BR mutant virus, in which 10 of the 13 positive residues of NC have been replaced with alanines and incorporation of viral genomic RNA is virtually abolished. We found that the mutations in the basic residues of NC did not disrupt Gag assembly at the cell membrane. The mutant Gag protein can assemble efficiently at the cell membrane, and viral proteins are detected outside the cell as efficiently as they are for the wild type. However, only approximately 10% of the Gag molecules present in the supernatant of this mutant sediment at the correct density for a retroviral particle. The reduction of positive charge in the NC basic domain of the M1-2/BR virus adversely affects both the specific and nonspecific RNA binding properties of NC, and thus the assembled Gag polyprotein does not bind significant amounts of viral or cellular RNA. We found a direct correlation between the percentage of Gag associated with sedimented particles and the amount of incorporated RNA. We conclude that RNA binding by Gag, whether the RNA is viral or not, is critical to retroviral particle integrity after cell membrane assembly and is less important for Gag-Gag interactions during particle assembly and release.

Outer and Central Charged Residues in DIVS4 of Skeletal Muscle Sodium Channels Have Differing Roles in Deactivation

We tested the effects of charge-neutralizing mutations of the eight arginine residues in DIVS4 of the rat skeletal muscle sodium channel (rNa V1.4) on deactivation gating from the open and inactivated states. We hypothesized that neutralization of outer or central charges would accelerate the I-to-C transition as measured by recovery delay because these represent a portion of the immobilizable charge. R1Q abbreviated recovery delay as a consequence of reduced charge content. R4Q increased delay, whereas R5Q abbreviated delay, and charge-substitutions at these residues indicated that each effect was allosteric. We also hypothesized that neutralization of any residue in DIVS4 would slow the O-to-C transition with reduction in positive charge. Reduction in charge at R1, and to a lesser extent at R5, slowed open-state deactivation, while charge neutralizations at R2, R3, R4, R6, and R7 accelerated open-state deactivation. Our findings suggest that arginine residues in DIVS4 in rNa V1.4 have differing roles in channel closure from open and inactivated states. Furthermore, they suggest that deactivation in DIVS4 is regulated by charge interaction between the electrical field with the outermost residue, and by local allosteric interactions imparted by central charges.

Altered Podzolization Resulting from Replacing Heather with Sitka Spruce

Podzolization processes were studied under heather (Calluna vulgaris L. Hull) and Crowberry (Empetrum nigrum L.) and sitka spruce [Picea sitchensis (Bong.) Carr] planted on former heathland at Hjelm Hede, Jutland, Denmark. The aim was to compare changes in soil‐water chemistry with changes in the solid‐state chemistry after vegetation change. Fourteen profiles under heather and five profiles under spruce were examined and soil water was collected in lysimeter wells from the bottom of individual soil horizons A, E, Bh, and Bs from four representative profiles. The investigated area has been heathland for more than 2000 yr and part of it was planted with sitka spruce in 1933. The sitka spruce litter provided a more acidic soil environment, and the taller canopy increased the deposition of seasalts. The acidifying effects were increased by increased evapotranspiration from the plantation compared with the heathland. The investigation indicates disturbance of the podzolization process under spruce. Soil‐water chemistry showed a lack of Al immobilization in the B horizon under spruce, contrary to the heather system. Analyses of the spruce soil reveal a depletion of pyrophosphate (PYR) extractable Al and Fe. The charge balance in soil water showed a high deficit of anions under spruce compared with the dissolved organic C (DOC) concentration. Therefore, the deficit cannot be exclusively ascribed to negative charge on DOC. Sources of anion deficit might include (i) dissociated organic acids (R‐COO−), (ii) reduction in positive charge because of the existence of organo‐metal complexes [R‐(COO)2Al+], and (iii) reduction in positive charge because of an inorganic pH‐dependent species distribution of Al [Al(OH)2+, Al(OH)+2

Modulatory effect of extracellular Mg 2+ ions on K + and Ca 2+ currents of capillary endothelial cells from rat brain

Using whole-cell patch-clamp recording, we demonstrate that exposure of single rat brain capillary endothelial cells to different extracellular Mg 2+ concentrations (0.3, 4.8 and 9.6 mM) affects the conductance of K + and Ca 2+ currents elicited under control conditions (1.2 mM). Extracellular Mg 2+ concentrations ([Mg 2+] o) of 4.8 and 9.6 mM reversibly depress outward K + currents by about 30 ± 12% ( n =10) and 3% ± 13%( n = 10), at all activating potentials, respectively. Using identical concentrations reversibly depressed the Ca 2+ current by about 40 ± 16% ( n = 8) and 46 ± 18% ( n = 6), respectively. Using a low Mg 2+ concentration of 0.3 mM, the K + current activation was unexpectedly and mildly increased by about 15 ± 5% ( n = 5), and the inward Ca 2+ current was attenuated. When studying this effect of low [Mg 2+] o on ‘pure’ Ca 2+ currents, free of outward currents, we found that this inward current was depressed by about 38 ± 16% ( n = 8), and its threshold for activation, in the current-voltage relationship, was shifted to more negative potentials. It is concluded that high [Mg 2+] o hinders the entry of Ca 2+ through low-voltage activated Ca 2+ channels and thereby attenuates a Ca 2+-regulated K + conductance. At a low [Mg 2+] o (0.3 mM), Mg 2+ shifts the steady-state inactivation of the voltage-activated Ca 2+ channel to more negative potentials by about 8 mV ( n = 6), probably due to a negative screening effect, i.e. a reduction of positive charges on the cell membrane. This may contribute to an apparent increase in K + conductance by an, as yet, unknown mechanism.

The effect of deamination and/or blocking arginine residues on the molecular assembly of acid-extracted rat tail tendon collagen

We describe the effect of deamination of lysine and blocking of arginine residues on the assembly of collagen into native fibrils and SLS aggregates. Treatment of collagen solutions with one or both of these procedures does not prevent the formation of fibrils or SLS aggregates but reduces their ability to form assemblies with accurate longitudinal registration. These observations provide direct confirmation that hydrophobic interactions are important in collagen assembly. Unbanded fibrils were formed within the first 24 h at 4°C from both acidic and neutralized deaminated and from neutralized control collagen solutions, transversely banded fibrils appearing later. This is compatible with the suggestion that initially, collagen fibrils are assembled by lyotropic liquid crystallization and with other observations which suggest that collagen molecules are initially free to move laterally within the fibril before being locked into place. Fibrils assembled from deaminated collagen solution show two variant longitudinal registration patterns which grade into one another. This suggests that, with a reduction in positively charged side chains, the thermodynamic energy minima responsible for longitudinal registration are less sharp compared with control collagen solutions. Reduction of positive charge by chemical modification helps to explain why the chemical modifications reduce swelling of collagen fibres. It also helps to explain why fibrils form spontaneously at 4°C in both arginine-blocked and deaminated collagen solutions. Thus chemical modifications of rat tail tendon provides new insight into the mechanisms in collagen assembly.

Cumulative site-directed charge-change replacements in bacteriophage T4 lysozyme suggest that long-range electrostatic interactions contribute little to protein stability

Bacteriophage T4 lysozyme is a basic molecule with an isoelectric point above 9·0, and an excess of nine positive charges at neutral pH. It might be expected that it would be energetically costly to bring these out-of-balance charges from the extended, unfolded, form of the protein into the compact folded state. To determine the contribution of such long-range electrostatic interactions to the stability of the protein, five positively charged surface residues, Lys16, Arg119, Lys135, Lys147 and Arg154, were individually replaced with glutamic acid. Eight selected double, triple and quadruple mutants were also constructed so as to sequentially reduce the out-of-balance formal charge on the molecule from +9 to +1 units. Each of the five single variant proteins was crystallized and high-resolution X-ray analysis confirmed that each mutant structure was, in general, very similar to the wild-type. In the case of R154E, however, the Arg154 to Glu replacement caused a rearrangement in which Asp127 replaced Glu128 as the capping residue of a nearby α-helix. The thermal stabilities of all 13 variant proteins were found to be fairly similar, ranging from 0·5 kcal/mol more stable than wild-type to 1·7 kcal/mol less stable than wild-type. In the case of the five single charge-change variants, for which the structures were determined, the changes in stability can be rationalized in terms of changes in local interactions at the site of the replacement. There is no evidence that the reduction in the out-of-balance charge on the molecule increases the stability of the folded relative to the unfolded form, either at pH 2·8 or at pH 5·3. This indicates that long-range electrostatic interactions between the substituted amino acid residues and other charged groups on the surface of the molecule are weak or non-existent. Furthermore, the relative stabilities of the multiple charge replacement mutant proteins were found to be almost exactly equal to the sums of the relative stabilities of the constituentn single mutant proteins. This also clearly indicates that the electrostatic interactions between the replaced charges are negligibly small. The activities of the charge-change mutant lysozymes, as measured by the rate of hydrolysis of cell wall suspensions, are essentially equal to that of the wild-type lysozyme, but on a lysoplate assay the mutant enzymes appear to have higher activity. This observation can be rationalized by assuming that the reduction of positive charge on T4 lysozyme does not affect the rate of catalysis, but does weaken the interaction between the negatively charged substrate and the positively charged C-terminal domain of the protein.

Re-evaluation of turbidimetry of proteins by use of aromatic sulfonic acids and chloroacetic acids.

From studies on 11 different proteins (including native albumin and albumin with reduced disulfide-bridges) treated with sulfosalicylic, 2-naphthalenesulfonic, toluenesulfonic, dichloroacetic, or trichloroacetic acids, we elucidate the interactions determining the resulting turbidities and other factors affecting turbidities, and we discuss the clinical utility of such turbidimetry. At least three interactions are important in determining turbidity: reduction of positive charges on the protein, hydrogen bonding of the non-ionized chloroacetic acids with the protein, and hydrophobic interaction of the aromatic sulfonic acids with albumin. Turbidity varies appreciably with the species of acid and protein, concentrations of acid, temperature, and standing time after acid is added. We conclude that this technique should be restricted to confirming proteinuria.

1180. Reduction of positive charge in SIO 2 layers by PbO : I C Szep and K Solt, International Conf Phys Chem Semiconductors Heterojunctions Layer Structure, Vol 4, Akademiai Kiado Budapest 1971, 205–211

1180. Reduction of positive charge in SIO 2 layers by PbO : I C Szep and K Solt, International Conf Phys Chem Semiconductors Heterojunctions Layer Structure, Vol 4, Akademiai Kiado Budapest 1971, 205–211